There are numerous cases where it is necessary to have a small vessel containing an homogeneous mixture of liquid oxygen and liquid nitrogen in a predetermined and precise proportion.
For example a liquid oxygen/nitrogen homogeneous mixture can be used for many life support appliances where it is important to provide to the worker a pure gas for him to breathe. In addition the liquid mixture can provide to the worker a non negligeable cooling power. Current manufacturing processes of liquid gas produce liquid oxygen on one hand and liquid nitrogen On the other hand. It looks easy at first to obtain the desired mixture by mixing the two components. But in fact it is very difficult since the association of the two liquids (oxygen and nitrogen) is not a simple mixture but more like a dissolution of one liquid into the other. This dissolution is not stable since the liquid nitrogen is more volatile than the liquid oxygen. This phenomenon leads to a rapid increase of the concentration of oxygen in the liquid mixture and a rapid increase of nitrogen in the gaseous mixture existing above the surface of the liquid mixture. Several solutions have been tested to obtain in a large container a large quantity of liquid air in order to fill from this large tank, smaller containers ready to be used. These types of solutions lead to a large waste of oxygen and nitrogen since it is necessary to empty and throw away regularly a large quantity of precious oxygen and nitrogen; in these cases it is necessary to waste and empty out regularly a large quantity of liquid since progressively the liquid gets richer and richer in oxygen and this liquid mixture is too rich in the oxygen and the entire liquid still available has to be dumped out and replaced by a new mixture having a correct proportion of oxygen. Typically large tanks have a capacity of 1 to 10 cubic meters. Variation of the oxygen concentration is about 2 percent every day. For example if you have to fill 2 small 10 liter containers every day with a mixture of 24.+-.1 percent of oxygen (76.+-.1 percent of nitrogen) from a 10 cubic meter tank, it is necssary to waste 9,980 liters of precious liquid every day in order to fill two 10 liters small containers. This phenonon makes the use of liquid air for small life support systems uneconomical and unaccessible to most potential users. Up to now the use of a large tank was mandatory in order to obtain a homogenous mixture containing a predetermined and precise concentration of oxygen.
Furthermore the transfer from the large tank to the small container is very difficult since the nitrogen has a tendency to become gas before the oxygen and to stay or directly go in the upperparts of the ducts and containers, modifying the concentration of liquid and gaseous mixture. This is an unacceptable threat to the safety of the men having to use this life support equipment since the concentration of the liquid air delivered may not be within the acceptable limits.